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The doctoral dissertation and master's thesis reflects the scholarly research in a graduate program as required for the completion of the degree at the University of Delaware.
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Browsing Graduate College by Author "Acharya, Himal"
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Item Mobilization of phosphorus from estuarine sediments in the Indian River Bay, Delaware(University of Delaware, 2023) Acharya, HimalPhosphorus (P) is often the limiting nutrient in freshwater ecosystems and can co-limit with nitrogen (N) in estuaries. Excess P can result in surface water eutrophication and bottom water hypoxia. Indian River estuary in Delaware has a long history of receiving a high discharge of nutrients from several point and non-point sources, and it served as a conduit to transport nutrients out to the Bay. The estuary has been suffering from water quality problems in the late spring and summer months, even after the non-point sources were almost completely removed in the mid-2000s. This situation raises questions about the potential role of legacy sediments releasing P and refueling eutrophication. This research carried out a series of laboratory erosion experiments to understand sediment erosion and P mobilization and salinity experiments to understand the role of changing salinity to mobilize P from sediments. ☐ Sediment erosion results obtained from the dynamic shear stress experiments on intact sediment cores showed that the erodibility was much higher on the freshwater end-member site sediments dominated with clay and organic matter rich and were freshly deposited than the saline end-member site rich in sandy sediments. Loosely sorbed P pools were found to be preferentially released at low shear stress and initial erosion events. Sediments from the freshwater site were found to release about four times more P than the saline site when subjected to an identical erosion condition. Results from batch salinity experiments show a significant P release at all salinity ranges tested (0-33 PSU). The P release generally decreased with increasing salinity, but the extent of the decrease was low in the saline end member site. The release of P substantially decreased over time- which could be due to the precipitation of P in the suspended sediment. A suite of competitive reactions, including adsorption, desorption, precipitation, and dissolution, could have played different roles in yielding observed results. Overall, these results indicate that sediment P could be a significant source of P in the water column and should be considered in water quality assessments.